persistent-nodemap: add a revlog.storage.persistent-nodemap.slow-path option As discussed during the sprint, we want to prevent user to get an unexpected performance regression when accessing a repository using "persistent-nodemap" without the associated Rust extension. We start by adding a config declaration and some documentation. Since "allow" is the current behavior, we don't need to add any code. The option possible value will come later. Note that we already have a `storage.revlog.nodemap.mode` option, but that option is a bit different. It does some warning and checking at revlog instantiation time. While we want something done at requirements checking time. Since we plan for new names and new config value names, we introduce a new option and will drop the old one later. Differential Revision: https://phab.mercurial-scm.org/D9758

persistent-nodemap: document storage.revlog.persistent-nodemap.mmap=no The feature is gaining public facing document, its options too. Differential Revision: https://phab.mercurial-scm.org/D9757

persistent-nodemap: rename the storage.revlog.nodemap.mmap option Since the feature is publicly known as "persistent-nodemap" this seems better to reference it as "persistent-nodemap" in related config too. So we rename the option to `storage.revlog.persistent-nodemap.mmap`. Differential Revision: https://phab.mercurial-scm.org/D9756

persistent-nodemap: document the feature in `hg help config.format` This is necessary before we advertise the feature more. Differential Revision: https://phab.mercurial-scm.org/D9755

persistent-nodemap: write down the sprint conclusion This write down the plan for turning feature that are only fast when the rust extension exists. Future changesets will implement it. Differential Revision: https://phab.mercurial-scm.org/D9754

persistent-nodemap: document the `devel.persistent-nodemap` option What it does is not obvious. Differential Revision: https://phab.mercurial-scm.org/D9753

copies: fix some comment in _filter The scenario the comment describes match case 6, not case 2. Differential Revision: https://phab.mercurial-scm.org/D9793

discovery: move some debug output closer to were it belong I assume these debug output, increment and comment drifted over time. Differential Revision: https://phab.mercurial-scm.org/D9800

discovery: add a discovery.grow-sample.rate This allow to control the effect of the growth rate on the discovery process while doing analysis. Differential Revision: https://phab.mercurial-scm.org/D9799

discovery: add a `devel', b'discovery.grow-sample` That option make it possible to disable the "sample growing" behavior when doing analysis and comparison. Differential Revision: https://phab.mercurial-scm.org/D9798